As smaller transistors are manufactured, the critical dimension (CD) or resolution of patterned features is becoming more challenging to produce. Self-aligned patterning needs to replace overlay-driven patterning so that cost-effective scaling can continue even after introduction of extreme ultra-violet (EUV) lithography. Patterning options that enable reduced variability, extend scaling and enhanced CD and process control are needed. Selective deposition of thin films such as void-free filling of fine recessed features is a key step in patterning in highly scaled technology nodes. However it's extremely challenging to fill trenches with retrograde profiles (bottle neck) with a material such that the trenches have no voids.
Silicon dioxide (SiO2) is the most common dielectric material in silicon microelectronic devices. However, despite its importance, void-free and seam-free filling of fine recessed features with SiO2 material has proved difficult to achieve at low temperatures. FIGS. 1A and 1B schematically show through cross-sectional views the problem of voids formed in a material when filling a recessed feature having a retrograde profile. FIG. 1A shows a recessed feature 104 with a retrograde profile formed in a film 102 on a base layer 100. The recessed feature 104 is extremely difficult to fill with a material such as SiO2 without forming any voids in the SiO2. FIG. 1B shows a void 108 that is formed in the SiO2 material when the opening of the recessed feature 104 is pinched off by the SiO2 that is being deposited. FIG. 2 shows a Scanning Electron Microscope (SEM) image of voids formed in SiO2 filling recessed features with retrograde profiles.
Void-free filling of fine recessed features is critical for many applications in semiconductor manufacturing. Many gap-fill applications depend on void-free SiO2 filling of fine recessed features, where the SiO2 needs to be of high quality and void-free, in order to provide the same etch rate throughout the entire thickness of the SiO2 fill.